High performance energy storage devices

ABSTRACT

A lead-acid battery comprising:
         at least one lead-based negative electrode;   at least one lead dioxide-based positive electrode;   at least one capacitor electrode; and   electrolyte in contact with the electrodes;
 
wherein a battery part is formed by the lead based negative electrode and the lead dioxide-based positive electrode; and an asymmetric capacitor part is formed by the capacitor electrode and one electrode selected from the lead based negative electrode and the lead-dioxide based positive electrode; and wherein all negative electrodes are connected to a negative busbar, and all positive electrodes are connected to a positive busbar.
       

     The capacitor electrode may be a capacitor negative electrode comprising carbon and an additive mixture selected from oxides, hydroxides or sulfates of lead, zinc, cadmium, silver and bismuth, or a capacitor negative electrode comprising carbon, red lead, antimony in oxide, hydroxide or sulfate form, and optionally other additives. The capacitor electrode may be used in asymmetric capacitors and batteries of other types.

This application is a continuation of application Ser. No. 10/571,255filed Jan. 10, 2007, now allowed, which in turn is the US national phaseof international application PCT/AU2004/001262 , filed 16 Sep. 2004 ,which designated the U.S. and claims priority of AU 2003905086, filed 18Sep. 2003, the entire contents of each of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

The present invention relates to high performance energy storagedevices, including batteries such as lead-acid batteries and otherbattery types, as well as capacitor electrodes and asymmetriccapacitors.

There is growing demand for the development and introduction of vehiclesthat do not rely almost entirely on fossil fuels, to combat airpollution in urban environments and to reduce the global consumption oflimited supplies of the fossil fuels. Such vehicles fall into three mainclasses: electric vehicles (EVs), hybrid electric vehicles (HEVs) andmild hybrid electric vehicles (also known as 42-volt powernet vehicles).

Electric vehicles and hybrid electric vehicles may use a variety ofdifferent battery types, including lead-acid batteries. Mild hybridelectric vehicles may use mainly lead-acid batteries because of reducedcost. Hybrid and mild hybrid electric vehicles rely on a combination ofan internal combustion engine and a battery for power supply. Due to theincreasing on-board power requirements in the present luxury cars(internal combustion engine cars), the capability of present 14-voltalternators is close to or beyond its limitation. Thus, mild hybridelectric vehicles have been developed. Such mild hybrid electricvehicles employ a 36-volt battery and a 42-volt alternator. The mildhybrid electric vehicles provide some advantages over the existinginternal combustion engine cars, including higher use of theelectrically generated power, resulting in lower emissions.

Whilst there have been many significant advances in the development ofnew batteries and power networks for vehicles relying at least partly onelectric power, the batteries used in these vehicles still suffer from anumber of problems.

In all of these batteries, different demands are placed on the batteryin terms of the current drawn from and recharged to the battery atvarious stages during vehicle operation. For example, a high rate ofdischarge is needed from the battery to enable acceleration or enginecranking in electric and hybrid electric vehicles, respectively. A highrate of recharging of the battery is associated with regenerativebraking.

In the situation where lead-acid batteries are utilised, particularly inhybrid and mild hybrid electric vehicles, the high rate of batterydischarging and recharging results in the formation of a layer of leadsulphate on the surface of the negative plate, and the generation ofhydrogen/oxygen at the negative and positive plates. This largely arisesas a result of high current demands on the battery. The partialstate-of-charge conditions (PSoC) under which these batteries generallyoperate is 20-100% for electric vehicles, 40-60% for hybrid electricvehicles, and 70-90% for mild hybrid electric vehicles. This is a highrate partial state-of-charge (HRPSoC). Under simulated HRPSoC duty, suchas hybrid and mild hybrid electric vehicle operations, the lead-acidbatteries fail prematurely mainly due to the progressive accumulation oflead sulphate on the surfaces of the negative plates. This occursbecause the lead sulphate cannot be converted efficiently back to spongelead during charging either from the regenerative braking or from theengine. Eventually, this layer of lead sulphate develops to such anextent that the effective surface area of the plate is reduced markedly,and the plate can no longer deliver the higher current demanded from theautomobile. This significantly reduces the potential life span of thebattery.

In other technology fields, including mobile or cell phone technology,it would be advantageous to provide alternative battery types that offerimproved overall lifespan and performance whilst catering for thedifferent power demands on the device.

Accordingly, there exists a need for modified batteries, includinglead-acid batteries, that have an improved life span and/or improvedoverall performance compared to current batteries.

SUMMARY OF THE INVENTION

According to one aspect, there is provided a lead-acid batterycomprising:

-   -   at least one lead-based negative electrode,    -   at least one lead dioxide-based positive electrode,    -   at least one capacitor negative electrode, and    -   electrolyte in contact with the electrodes,        wherein the positive electrode and the lead-based negative        electrode define a battery part, and the positive electrode and        the capacitor negative electrode define an asymmetric capacitor        part, with the positive electrode shared by the battery part and        the asymmetric capacitor part, and wherein the lead-based        negative and capacitor negative electrodes are connected to a        negative busbar, and the positive electrode or electrodes are        connected to a positive busbar.

Thus, the lead dioxide battery part and the asymmetric capacitor part ofthe lead-acid battery are connected in parallel in the one common unit.Hence, the asymmetric capacitor part preferentially takes or releasescharge during high current charging or discharging. This occurs sincethe asymmetric capacitor part has a lower internal resistance than thebattery-part, and will first absorb and release charge during high-ratecharging (for instance during regenerative braking) or during high-ratedischarging (for instance during vehicle acceleration and enginecranking). Consequently, the asymmetric capacitor part will share thehigh-rate operation of the lead-acid battery part, and will provide thelead-acid battery with significantly longer life. All of this isachieved without any electronic control or switching between the batteryand capacitor parts.

According to one embodiment, the positive electrode shared by the twoparts is disposed between the lead-based negative electrode and thecapacitor negative electrode.

It will be appreciated that the reverse arrangement may be utilised, inwhich the shared electrode is the lead-based negative electrode. Thelead-based negative electrode will define an asymmetric capacitor partwith a capacitor positive electrode.

Thus, allowing for the two alternative arrangements, a second aspectprovides a lead-acid battery comprising:

-   -   at least one lead-based negative electrode;    -   at least one lead dioxide-based positive electrode;    -   at least one capacitor electrode; and    -   electrolyte in contact with the electrodes;        wherein a battery part is formed by the lead based negative        electrode and the lead dioxide-based positive electrode; and an        asymmetric capacitor part is formed by the capacitor electrode        and one electrode selected from the lead based negative        electrode and the lead dioxide based positive electrode; and        wherein all negative electrodes are connected to a negative        busbar, and all positive electrodes are connected to a positive        busbar.

According to this aspect, each of the capacitor electrodes mayindividually be positive or negative electrodes.

Preferably, the lead-acid battery comprises an alternating series ofpositive and negative electrodes. Of the alternating electrodes, each ofthese may be a battery electrode, a capacitor electrode, or a combinedbattery/capacitor electrode. These electrode types will be described infurther detail below.

According to a third aspect of the present invention, there is provideda lead-acid battery comprising an alternating series of positive andnegative electrodes and an electrolyte in contact with the electrodes,wherein:

-   -   at least one pair of adjacent positive and negative electrode        regions store energy capacitively, and    -   at least one pair of adjacent lead dioxide positive and lead        negative battery electrode regions store energy        electrochemically,        and wherein the positive electrodes are directly connected by a        first conductor and the negative electrodes are directly        connected by a second conductor.

In a further aspect of the invention, it has been found that if there isa mismatch in the potential window or potential operational range of oneof the electrodes, hydrogen gassing may occur. This particularly applieswhen the cell voltage is greater than the potential range of anelectrode. Hydrogen gassing is undesirable as it leads to prematurefailure of the battery at the electrode where gassing occurs.

To avoid a mismatch, according to a further embodiment, at least one ofthe capacitor negative electrodes comprises a high surface areacapacitor material and one or more additives selected from oxides,hydroxides or sulfates of lead, zinc, cadmium, silver and bismuth. Theadditives are preferably added in oxide form. The additives arepreferably lead and/or zinc additives, most preferably lead and/or zincoxide.

Mismatching can also occur at the capacitor positive electrode. Thus,according to one embodiment in which the battery comprises a capacitorpositive electrode, the capacitor positive electrode comprises:

-   -   a high surface area capacitor material,    -   Pb₂O₃,    -   an oxide, hydroxide or sulfate of antimony, and    -   optionally one or more additives selected from oxides,        hydroxides and sulfates of iron and lead.

This aspect of the invention can be applied equally to other hybridbattery types to avoid gasing.

Thus, according to a fourth aspect of the invention, there is provided ahybrid battery-capacitor comprising:

-   -   at least one battery-type positive electrode,    -   at least one battery-type negative electrode,    -   at least one capacitor-type electrode selected from a capacitor        negative electrode and a capacitor positive electrode, wherein        the capacitor negative electrode comprises a high surface area        capacitor material and one or more additives selected from        oxides, hydroxides or sulfates of lead, zinc, cadmium, silver        and bismuth, and wherein the capacitor positive electrode        comprises:        -   a high surface area capacitor material,        -   Pb₂O₃,        -   an oxide, hydroxide or sulfate of antimony, and        -   optionally one or more additives selected from oxides,            hydroxides and sulfates of iron and lead, and    -   an electrolyte in contact with the electrodes, wherein a battery        part is formed between (i.e. defined by) the battery-type        positive electrode and the battery-type negative electrode, and        an asymmetric capacitor part is formed between the capacitor        electrode and one of the battery-type electrodes, wherein one of        the battery-type electrodes shared by the battery part and the        asymmetric capacitor part, and wherein the negative electrodes        are in direct electrical connection to a first conductor, and        the positive electrodes are in direct electrical connection to a        second conductor.

According to a further aspect of the invention, there is also providednovel capacitor electrodes based on the above concept. The novelcapacitor negative electrode comprises a current collector and a pastecoating, the paste coating comprising a high surface area capacitormaterial, a binder and between 5-40 wt %, based on the weight the pastecoating, of an additive or additive mixture selected from oxides,hydroxides or sulfates of lead, zinc, cadmium, silver and bismuth, withthe proviso that the additive includes at least one oxide, hydroxide orsulfate of lead or zinc.

The novel capacitor positive electrode comprises a current collector anda paste coating, the paste coating comprising a high surface areacapacitor material, a binder and between 10-40 wt %, based on the weightthe paste coating, of an additive mixture comprising:

-   -   Pb₂O₃,    -   an oxide, hydroxide or sulfate of antimony, and    -   optionally one or more oxides, hydroxides or sulfates of iron        and lead.

Finally, there is also provided an asymmetric capacitor comprising thecapacitor electrodes described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a lead-acid battery in accordancewith one embodiment of the invention;

FIG. 2 is a schematic plan view of the lead-acid battery of FIG. 1;

FIG. 3 is a graph representing a current profile of a single cycle ofthe test conducted on the battery of the embodiment of FIGS. 1 and 2;

FIG. 4 is a graph representing the cycling performance of the battery ofFIGS. 1 and 2 against a comparison battery;

FIG. 5 is a schematic side view of a lead-acid battery in accordancewith a second embodiment of the invention;

FIG. 6 is a schematic side view of one of the negative electrodes of thelead-acid battery of FIG. 5;

FIG. 7 is a graph representing the hydrogen evolution rate of a negativecapacitor electrode of a fourth embodiment of the invention, compared toa standard carbon electrode and a standard lead-based negativeelectrode;

FIG. 8 is a schematic side view representing the electrode arrangementof a battery of a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in further detail withreference to preferred embodiments of the invention.

To avoid any doubt, except where the context requires otherwise due toexpress language or necessary implication, the word “comprise” orvariations such as “comprises” or “comprising” is used in an inclusivesense, i.e. to specify the presence of the stated features but not topreclude the presence or addition of further features in variousembodiments of the invention.

General Features

The term “lead-acid battery” is used in its broadest sense to encompassany unit containing one or more lead-acid battery cells.

The lead-acid batteries described contain at least one lead-basednegative electrode or region, at least one lead dioxide-based positiveelectrode or region and at least one capacitor negative electrode orregion.

In the following each of these electrode types are described, followedby the electrode region concept.

Electrode Structure

Electrodes generally comprise a current collector (otherwise known as agrid or plate), with the active electrode material applied thereto. Theactive electrode material is most commonly applied in a paste form tothe current collector, and in the present specification the term pasteapplies to all such active-material containing compositions applied inany way to the current collector. The term “based” used in the contextof electrodes is intended to refer to the active electrode material.This term is used to avoid suggesting that the electrode is formedentirely from the active material, as this is not the case. The termalso is intended to indicate that the active material of the givenelectrode may contain additives or materials other than the activematerial specifically mentioned.

Lead and Lead Dioxide Based Electrodes.

The lead and lead dioxide electrodes may be of any arrangement or typesuitable for use in a lead-acid battery. Generally, such electrodes arein the form of a metal grid (usually made from lead or lead alloy) thatsupports the electrochemically active material (lead or lead dioxide)which is pasted onto the grid. The operation of pasting is well known inthe field. Although any suitable lead or lead dioxide known in the artmay be used, it would be advantageous to use the lead compositionsdisclosed in co-pending application PCT/AU2003/001404 (claiming priorityfrom Australian Patent Application AU 2002952234). It is to be notedthat, prior to formation of the battery, the active material may not bein the active form (i.e. it may not be in the form of the metal, or inthe dioxide form). Thus, the terms encompass those other forms which areconverted to lead metal or lead dioxide when the battery is formed.

Capacitor Electrodes

Capacitor electrodes similarly comprise a current collector and acoating of an active material. This is commonly applied as a paste.

The term “capacitor” is used in the context of electrodes to refer toelectrodes that store energy through the double layer capacitance of aparticle/solution interface between high surface area materials and anelectrolyte solution.

There are two main classes of capacitors. One class is the “double-layercapacitors” (otherwise known as “symmetric capacitors”) containing twosuch electrodes, one as the positive and the other as the negative. Thesecond class is the asymmetric capacitors, which are also referred to ashybrid capacitors, “ultracapacitors” and “supercapacitors”.

Asymmetric capacitors comprise one electrode that stores energy throughdouble layer capacitance across a particle/solution interface, and asecond electrode that is a faradaic or battery-type electrode whichstores energy pseudocapacitively. The prefixes “ultra” and “super” aresometimes used to refer generically to asmymmetric capacitors, andsometimes to refer to such capacitors having large storage capability.In the present application the prefix “ultra” is most usually used inthis first sense, but on occasion it is used in the second sense, as thecapacitance of the capacitor parts of the batteries of the presentinvention preferably have high capacitance. The asymmetric capacitorparts preferably have ultracapacitor capacitance, more preferably ofsupercapacitor capacitance.

Generally, as with the lead and lead oxide electrodes, the capacitorelectrode comprises a metal grid (usually made from a lead alloy) and apasted coating containing the capacitor material, usually with a binder.Examples of a suitable binders for the paste compositions arecarboxymethyl cellulose and neoprene.

The capacitor electrode suitably comprises a high surface area (orhigh-rate) materials suitable for use in capacitors. Such materials arewell known in the art. These high-rate capacitor materials include highsurface area carbon, ruthenium oxide, silver oxide, cobalt oxide andconducting polymers. Preferably, the capacitor negative electrodecomprises a high surface area carbon material. Examples of high surfacearea carbon materials are activated carbon, carbon black, amorphouscarbon, carbon nanoparticles, carbon nanotubes, carbon fibres andmixtures thereof.

Often mixtures of materials are used to obtain an appropriate balancebetween surface area (and thus capacitance) and conductivity. Currently,for cost reasons, activated carbon is the most appropriate source. Onesuitable activated carbon material is one with a surface area of between1000 and 2500 m²/g, preferably 1000-2000 m²/g. This material is suitablyused in combination with a more conductive material, such as carbonblack. One suitable carbon black material has a surface area of between60-1000 m²/g. One suitable mixture of these materials comprises between5-20% carbon black, 40-80% activated carbon, 0-10% carbon fibres, andthe balance binder at a level of between 5-25%. All measurements are byweight unless specified otherwise.

Additive Content of Capacitor Electrodes

As described above, it has been found that if there is a mismatch in thepotential window or potential operational range of one of theelectrodes, hydrogen and/or oxygen gassing may occur. According to oneembodiment, to suppressing hydrogen gassing, the capacitor negativeelectrodes comprise an additive or additive mixture comprising an oxide,hydroxide or sulfate of lead, zinc, cadmium, silver and bismuth, or amixture thereof. Generally, it is preferred that the additive includesat least one oxide, hydroxide or sulfate of lead or zinc. Forconvenience, the additive is suitably one or more oxides selected fromlead oxide, zinc oxide, cadmium oxide, silver oxide and bismuth oxide.Preferably each of the capacitor negative electrodes comprise theadditive in addition to the high surface area capacitor material. Due totoxicity reasons, cadmium compounds are not preferred, and therefore thecomposition preferably comprises a lead compound and/or zinc compound,and optionally a silver compound. For cost reasons, silver oxide andbismuth oxide would usually be avoided.

Irrespective of the form in which the additive is added, when conductorcomes into contact with the electrolyte (for example, sulfuric acid),the additive may react with the electrolyte and thus be converted intoanother metal compound derived from the original metal oxide, sulfate orhydroxide. References to the oxides, sulfates and hydroxides of thesubject additives are to be read as encompassing the products of thereactions between the additives and the electrolyte. Similarly, ifduring the charged or discharged state of the battery the additive isconverted into another form through redox reactions, the references tothe oxides, sulfates and hydroxides are to be read as encompassing theproducts of the redox reactions on these additives.

To suppressing oxygen gassing, the capacitor positive electrodespreferably comprises:

-   -   a high surface area capacitor material (as described above),    -   Pb₂O₃ (“red lead”),    -   an oxide, hydroxide or sulfate of antimony, and    -   optionally one or more additives selected from oxides,        hydroxides and sulfates of iron and lead.

The compound of antimony is beneficial in suppressing (oxygen) gassingat the positive capacitor electrode. However, if it migrates to thenegative capacitor electrode, it produces an adverse effect on hydrogengassing at that electrode. In the absence of an agent to fix theantimony compound to the positive capacitor electrode, when the antimonycompound comes into contact with the electrolyte, it may dissolve in theelectrolyte, and be deposited on the negative electrode when a currentis applied. The red lead is used to fix or prevent transfer of theantimony to the negative electrode. Compounds (i.e. oxides, sulfates orhydroxides) of lead and iron are also advantageous in this electrode,and may also be used in the additive mixture.

In each case, the additive is used in amount to avoid hydrogen andoxygen gassing. This is generally an amount that increases the potentialwindow of the capacitor negative and positive electrode from the typical±0.9V or ±1.0V to at least ±1.2V, and preferably at least ±1.3V. Ingeneral terms, the total oxide content may be between 5-40 wt %, basedon the total active material composition (including high surface activematerial, binder, and any other component in the dried pastecomposition).

Preferably, the negative capacitor electrode additive comprises between1-40 wt % Pb compound (more preferably 1-20%), 1-20 wt % Zn compound(more preferably 1-10%), 0-5 wt % Cd compound and 0-5 wt % Ag compound.Preferably the total is within the 5-40 wt % range mentioned above. Theuse of ZnO additive alone provides good results, as does PbO alone, or amixture of PbO and ZnO.

Preferably, the positive capacitor electrode additive comprises between0-30 wt % Pb (preferably 1-30 wt %) in oxide (any oxide), sulfate orhydroxide form, 1-10 wt % Pb₂O₃, 0-2 wt % Fe (preferably 1-2 wt %) inoxide, sulfate or hydroxide form and 0.05 to 1 wt % Sb in oxide, sulfateor hydroxide form. Preferably Sb is added as an oxide. Preferably thetotal is within 5-40 wt % range mentioned above.

Other Applications for Capacitor Electrodes

The additive-containing capacitor electrodes may be used with a batterytype electrode (lead or lead dioxide) and an electrolyte to form anasymmetric capacitor, without any battery positive and battery negativeelectrode pair defining a battery part. This asymmetric capacitorcontaining novel components can be externally connected to a battery inthe conventional manner, but without any extra electronic device.

Other Electrodes

As described in further detail below, the battery may include electrodesof other types in addition to or as a replacement of the electrodesdescribed above. In particular, the battery may comprise one or moremixed capacitor-battery electrodes, such as a capacitor-battery positiveelectrode.

In the situation where the capacitor positive electrode (as describedabove) comprises lead oxide, this is converted into lead dioxide duringcharging of the battery. Thus, the capacitor electrode comprising a leadsource which is converted into lead dioxide in operation of the batterymay be considered to be a capacitor-battery electrode having somequalities of both a capacitor electrode and a battery electrode.

The incorporation of high surface area material such as carbon into somepositive electrodes may be undertaken to address the need to balance thesurface area ratio of the positive to negative electrodes. In theabsence of any capacitor positive electrodes, the high surface areacapacitor negative electrodes will add to a greater overall surface areafor negative electrodes compared to positive electrodes. When there is asurface area imbalance, failure of the lower surface area electrodes. Bymaking the surface area of the positive electrode greater, byincorporating high surface area carbon into some positive electrodes,the balance is addressed.

As a consequence of the above, it will be appreciated to persons in theart that the battery may comprise an alternating series of positive andnegative electrodes, with an electrolyte in contact with the electrodes,and a first conductor for directly connecting the positive electrodesand a second conductor for directly connecting the negative electrodes,wherein at least one pair of the adjacent positive and negativeelectrode regions form a capacitor (by storing capacitive energy), andat least one pair of adjacent positive and negative electrode regionsform a battery (by storing energy as electrochemical potential betweenthe two electrode pairs).

Regions

The electrodes of the present invention may be composite electrodes(i.e. they may be composites of battery electrode materials andcapacitor electrode materials). The references to “lead-based”, “leaddioxide-based” and “capacitor” electrodes encompass the regions of anelectrode that have the specified function, irrespective of whether ornot the single electrode has other regions of a different type.

According to one embodiment of the invention, electrodes having regionsof different types are deliberately used. According to this embodiment,one or more of the negative electrodes has at least two regions,including a battery-electrode material region and a capacitor-electrodematerial region. As one example, the electrode having two regionscomprises an electrode current collector, which may be of the typedescribed above, having one face pasted with battery electrode material(such as lead) and the opposite face pasted with capacitor negativeelectrode material. Alternatively, a battery-type electrode containingbattery electrode material on both sides may be coated on one face orany other region thereof by a capacitor electrode material.

Other Battery Electrode Types

According to the aspect of the invention in which the capacitorelectrode comprises carbon with an additive to avoid hydrogen gassing,the battery electrodes may be of types other than lead lead-acid batteryelectrodes. The battery types of this embodiment are nickel rechargeablebatteries, lithium metal or lithium ion rechargeable batteries, and soforth. Suitable battery-type positive electrode materials in this caseinclude nickel oxide, silver oxide, manganese oxide, lithium polymermaterials, mixed lithium oxides including lithium nickel oxides, lithiumcobalt oxides, lithium manganese oxides and lithium vanadium oxides, andlithium conductive polymer cathode materials. Suitable battery-typenegative electrode materials in this class include zinc, cadium, metalhydrides, lithium in metal or alloy form with other metals such asaluminium, and lithium ion intercalation materials. The details of, andalternatives for, these electrode materials used in various batterytypes can be gathered from various publications in the art of theinvention.

Physical Configuration

The electrodes may be of any suitable shape, and therefore may be inflat-plate form or in the form of a spirally-wound plate for theformation of either prismatic or spirally-wound cells. For simplicity ofdesign, flat plates are preferred.

Electrolyte

In the case of lead-acid batteries, any suitable acid electrolyte may beused. The electrolyte may, for instance, be in the form of a liquid or agel. Sulphuric acid electrolyte is preferred.

In the case of other battery types, the electrolyte may be an aqueous ororganic electrolyte, including alkalis such as potassium and otherhydroxides, lithium-ion containing organic solvents, polymerelectrolytes, ionic liquid electrolytes in liquid or solid state and soforth. Suitable electrolytes for the chosen battery positive andnegative electrode materials can be routinely selected by a personskilled in the art.

Busbars or Conductors

The busbar of the lead-acid battery may be of any suitable construction,and may be made from any suitable conductive material known in the art.The term “connected to” used in the context of the busbars refers toelectrical connection, although direct physical contact is preferred. Inthe case where the battery is not of a typical lead-acid batteryconfiguration with busbars, any conductor may be used that does notinvolve circuitry external to the battery.

Other Battery Features

Generally, the components of the battery will be contained within abattery case with further features appropriate to the type of batteryemployed. For example, in the case of lead-acid batteries, the lead-acidbattery may be either of a flooded-electrolyte design or of avalve-regulated design. Where the lead-acid battery is a valve-regulatedlead-acid battery, the battery may be of any suitable design, and mayfor instance contain gel electrolyte. Specific features of the batteryunit appropriate to such designs are well known in the art of theinvention.

The pressure that may be applied to the lead-acid battery may lie in therange of 5-20 kPa for flooded electrolyte design, and from 20-80 kPa forvalve regulated lead-acid battery design.

Separators

Generally, each of the positive and negative electrodes is separatedfrom adjacent electrodes by porous separators.

The separators maintain an appropriate separation distance betweenadjacent electrodes. Separators located between immediately adjacentlead-based negative electrodes and lead dioxide-based positiveelectrodes may be made from any suitable porous material commonly usedin the art, such as porous polymer materials or absorptive glassmicrofibre (“AGM”). The separation distance (corresponding to separatorthickness) is generally from 1-2.5 millimetres for these separators.Suitable polymer materials useful for forming the separators between thepositive and negative electrodes forming the battery part arepolyethylene and AGM. Polyethylene separators are suitably between 1 and1.5 millimetres thick, whereas AGM separators are appropriately between1.2 and 2.5 millimetres thick.

In the case of separators located between the positive electrode and thecapacitor negative electrode, these are suitably much thinner than theseparators of the battery part of the lead-acid battery. Advantageously,the separators are between 0.01 and 0.1 millimetres thick, and mostpreferably between 0.03 and 0.07 millimetres thick. These separators aresuitably made from microporous polymer material such as microporouspolypropylene. Other separators are AGM and the thickness of this typeof separators is between 0.1 and 1 millimetres, and preferably between0.1 and 0.5 millimetres.

Formation of Lead Acid Batteries

After assembling of the appropriate components together in a batterycase, the lead-acid battery generally needs to be formed. The formationoperation is well known in the field. It is to be understood that thereferences to “lead-based” and “lead dioxide-based” materials are usedto refer to lead or lead dioxide itself, materials containing themetal/metal dioxide or to materials that are converted into lead or leaddioxide, as the case may be, at the given electrode.

As is indicated by the language used above, the lead-acid batterycontains at least one of each type of electrode. The number ofindividual cells (made up of a negative and positive plate) in thebattery depends on the desired voltage of each battery. For a 36-voltbattery appropriate for use as a mild hybrid electric vehicle battery(which may be charged up to 42 volt), this would involve the use of 18cells.

Electrode Arrangement

For best operation according to one embodiment, the positive andnegative electrodes are interleaved, so that each positive electrode hasone lead-based negative electrode to one side of it, and one capacitornegative electrode to the opposite side. Accordingly, the arrangement ofone embodiment has alternating positive and negative electrodes, withthe negative electrodes being alternately a lead-based electrode and acapacitor negative electrode. All of the negative electrodes (lead andcarbon) are connected to the negative busbar, and the positiveelectrodes are connected to the positive busbar, so that each batterycell and ultracapacitor cell is connected in parallel in the commonlead-acid battery.

Operation

As explained above, the ultracapacitor cell in the lead-acid batteryarrangement described has a lower internal resistance than the lead-acidbattery cell, and therefore it will first absorb a release charge duringhigh-rate charging (for generative braking) or during high-ratedischarge (vehicle acceleration and engine cranking). Consequently, theasymmetric capacitor cell will share the high-rate operation of thelead-acid battery cell and will provide the lead-acid battery withsignificantly longer life. More specifically, lead sulphate formation onthe battery cell electrodes which generally occurs during high-currentcharging and discharging of the battery is minimised because thehigh-current charging and discharging is generally taken up by theasymmetric capacitor.

Each battery cell of one embodiment of the invention provides a voltageof 2-volts. A lead-acid battery of one embodiment suitable for use inthe broad range of electric vehicle battery applications will contain 8negative electrodes and 9 positive electrodes, with 4 of the negativeelectrodes being lead-based negative electrodes, and the other 4 beingcapacitor electrodes, in an alternating arrangement. Variations in thisarrangement and relative numbers of electrodes are also suitable,provided that there is a minimum of one of each electrode.

EXAMPLES Example 1

A lead-acid battery of one embodiment of the invention suitable fortesting purposes was made in the arrangement as illustratedschematically in FIGS. 1 and 2.

Two sponge lead (negative plate) electrodes (1), two lead dioxidepositive plate electrodes (2) and one high surface-area negative carbonelectrode plate (3) were positioned in an alternating arrangement asillustrated in FIG. 1 in a battery case (4). The positive lead dioxideelectrodes (2) and negative lead electrodes (1) were 40 millimetres wideby 68 millimetres high by 3.3 millimetres thick. The carbon electrode(3) was 40 millimetres wide by 68 millimetres high by 1.4 millimetresthick. The battery electrodes were of a standard configuration andcomposition for lead-acid batteries, and were made by the methodsdescribed in the detailed description above. The lead electrodeformation techniques used in this example are more fully described inour copending application PCT/AU2003/001404, the entire contents ofwhich are incorporated by reference. In brief, the paste composition forthe lead negative electrode comprised lead oxide (1 kg), fibre 0.6 g,BaSO₄ 4.93 g, Carbon black 0.26 g, H₂SO₄ (1.400 rel.dens.) 57 cm³, water110 cm³, acid to oxide ratio 4% and paste density 4.7 g/cm³. The pastecomposition for the lead dioxide positive electrode comprised lead oxide1 kg, fibre 0.3 g, H₂SO₄ (1.400 rel.dens.) 57 cm³, water 130 cm³, acidto oxide ratio 4% and paste density 4.5 g/cm³. The lead oxide wasconverted into lead dioxide and lead by the formation techniquesdescribed in our co-pending application.

The capacitor electrode (3) was made from 20 wt % carbon black withspecific surface area of 60 m² g (Denki Kagaku, Japan), 7.5 wt %carboxymethyl cellulose, 7.5 wt % neoprene, and 65 wt % activated carbonwith specific surface area of 2000 m² g⁻¹ (Kurarekemikaru Co. Ltd.Japan).

Separators (5, 6) were located between the adjacent electrodes.Absorptive glass microfibre (AGM) separators (5) of 2 millimetres inthickness were positioned between the lead-dioxide (2) and lead (1)electrodes, and microporous polypropylene separators (6) of 0.05millimetres thickness were sandwiched between the positive electrodes(2) and carbon electrode (3).

The battery case (4) was filled with sulfuric acid solution (7). Thepositive electrodes were connected to a positive busbar (8), and thenegative electrodes connected to a negative busbar (9). As noted below,for comparison purposes, for simulation of a battery containing noultracapacitor cell component, the capacitor negative plate could bedisconnected from the negative busbar.

For testing purposes, a charging and discharging profile was developedto simulate typical charge and discharge demands on a 42-volt mild HEVbattery typically used in mild HEV applications. The profile has shortduration (2.35 minutes) and is composed of several current steps thatsimulate the power requirements of the battery during vehicle operation.These are, in order:

-   -   (a) an idle stop section involving a discharge of 2 A over a 60        second period;    -   (b) a high current discharge of 17.5 A, lasting 0.5 seconds,        simulating cranking;    -   (c) an 8.5 A power assistance discharge of 0.5 seconds;    -   (d) a 14-volt/2 A maximum, 70 second long engine charging        section simulating charging of the battery during standard        driving conditions;    -   (e) a 5 second rest period; and    -   (f) a 14-volt/2 A maximum period correlating to regenerative        charging (regenerative braking) lasting 5 seconds.

The critical step is the cranking period over which the cell mustdeliver a current of 17.5 A for 0.5 seconds.

Testing

To test the life span of the battery of the example, two identicalbatteries were made, and one was thereafter modified to disconnect thecapacitor carbon negative electrode from the negative busbar, tocorrespond to an equivalent battery without the integral ultracapacitorfeature, hereafter referred to as the “comparison battery”.

Each battery was subjected to repeated cycles of the profile illustratedin FIG. 3 and described above. A cut-off voltage of 1.6-volts, which isa common cut-off voltage value for batteries in the field of theinvention, was set, and the batteries were subjected to repetitivecycling through the charge cycle until the lowest voltage duringdischarge reached the cut-off value.

The results of the test are illustrated in FIG. 4. In this figure, line10 is the comparison battery internal resistance profile, line 11 is theExample 1 battery internal resistance profile, line 12 is the comparisonbattery minimum discharge voltage profile and line 13 is the Example 1battery minimum discharge voltage profile.

During cycling, the following observations were made:

-   -   (i) the maximum charge voltages of the comparison battery and        the battery of Example 1 are maintained at 2.35-volts, as        represented by line 14.    -   (ii) the internal resistances of both batteries increase with        cycling. Nevertheless, the internal resistance of the comparison        battery increases faster than that of the battery of Example 1,        for example, from 19 to 25 mΩ for the comparison battery and        from 18 to 25 mΩ for the battery of Example 1.    -   (iii) The minimum discharge voltages of the comparison battery        and the battery of Example 1 decrease with cycling, but the rate        of decrease is faster for the comparison battery.

The comparison battery performs about 2150 cycles, while the battery ofExample 1 performs 8940 cycles before the minimum discharge voltages ofeach battery reaches the cut-off value of 1.6-volts (represented by line15. Thus, the cycling performance of the battery of Example 1 is atleast four times better than that of the comparison battery.

Example 2

A variation on the battery of Example 1 is illustrated in FIGS. 5 and 6.For ease of comparison, the same numerals are used to refer to commonfeatures of the two batteries.

The embodiment of this Example comprises three lead dioxide positiveplate electrodes (2) and two composite negative electrodes (16). Thecomposite negative electrodes comprise a current collector or grid (17)with the lead-containing paste composition described above applied toone region (the face) thereof (18) and capacitor high surface-areacarbon electrode material-containing paste applied to the opposite face(19). Formation of the electrode is conducted in the manner known in theart. In a variation on this embodiment that is simpler to manufacture, alead based negative electrode is prepared with lead pasted byconventional dipping techniques to the main body section in lead pastematerial, followed by formation, and then the capacitor material ispasted to a region or regions of this lead based negative electrode,such as one face thereof. The positive (2) and negative compositeelectrodes (16) are positioned in an alternating arrangement asillustrated in FIG. 5 in a battery case (4).

The positive lead dioxide electrodes (2) and negative compositeelectrodes (16) of the embodiment illustrated in FIG. 5 are 40millimetres wide by 68 millimetres high by 3.3 millimetres thick. Thecarbon electrode region (19) of the negative electrode takes up 1.4millimetres of the thickness of the negative electrode.

Separators (5, 6) are located between the adjacent electrodes.Absorptive glass microfibre (AGM) separators (5) of 2 millimetres inthickness are positioned between the lead-dioxide (2) and lead face (18)of the negative electrode, and microporous polypropylene separators (6)of 0.05 millimetres thickness are sandwiched between the positiveelectrodes (2) and carbon face of the negative electrode (19).

The battery case (4) is filled with sulfuric acid solution (7). Thepositive electrodes are connected to a positive busbar (8), and thenegative electrodes connected to a negative busbar (9).

Example 3

Further testing on the battery of Example 1 showed that improvements inelectrolyte dry-out could be achieved by matching the hydrogen evolutionrate of the carbon electrode (3) during battery charging to be similarto that of the lead negative electrode (1). This was achieved byreplacing the carbon electrode of Example 1 with a modified carbonelectrode (103) with 2.5 wt % PbO and 2.5 wt % ZnO, 65 wt % activatedcarbon, 20 wt % carbon black and binder (10 wt %) in the pastecomposition.

The hydrogen evolution rates for this electrode were tested and comparedto the electrode used in Example 1, as well as the hydrogen evolutionrates of the lead negative electrode of example 1. The results are shownin FIG. 7, in which curve 20 represents the carbon electrode hydrogenevolution rate, curve 21 represents the lead-acid negative platehydrogen evolution rate, and the curve 22 represents the carbon plusadditives electrode hydrogen evolution rate. The higher current densitylevels recorded for the carbon electrode with no oxide additive riseconsiderably at potentials falling below −1.2V, and even more so by−1.3V. By more closely matching the hydrogen evolution rate of the twoelectrodes, the battery can be operated at higher potentials withoutearlier failure due to electrolyte dry-out.

Inclusion of the oxide CdO would have a similar effect to ZnO and PbO,but for toxicity reasons was not used in the testing. Ago has a similareffect, but is an expensive additive and not as effective on its own. Inother tests the levels of ZnO and PbO were varied within the range 1-10%and 1-20% respectively, and the AgO between 1-5%. The other oxidesmentioned in the detailed description above have a similar impact toAgO.

Example 4

A further variation on the battery of Example 1 is illustrated in FIG.8. For ease of comparison, the same numerals are used to refer to commonfeatures of the two batteries. In addition, for simplicity, only thebattery electrodes are illustrated. It will be understood that thebattery further includes the separators, case, electrolyte, busbars,terminals and other features of batteries common in the art.

The battery of this Example comprises an alternating series of positiveand negative electrodes. The electrodes are, in order from left toright, a lead dioxide battery positive electrode (2), a lead-basedbattery negative electrode (3), a second lead dioxide battery positiveelectrode (2), a capacitor carbon and additive negative electrode of thetype described in Example 3 (103), a capacitor-battery positiveelectrode as described further below (23), a second capacitor carbon andadditive negative electrode of the type described in Example 3 (103), asecond lead based battery negative electrode (3) and a third leaddioxide battery positive electrode (2). Each of the positive andnegative electrodes, respectively, are connected to a positive conductorand a negative conductor, and to the positive and negative terminals ofthe battery.

The capacitor-battery electrode (23) comprises a metal currentcollector, with a mixture of activated carbon (60 wt %), carbon black(20 wt %) and 10 wt % of lead oxide pasted thereon. The pastecomposition is formed with 10 wt % [5 wt % carboxymethyl cellulose and 5wt % neoprene] binder and sintered onto the current collector. Theelectrode is about 0.8 mm thick. In gassing tests it was shown that theinclusion of SbO and red lead in this capacitor positive electrode hasan advantageous effect on gassing, and therefore these additives mayfurther be contained in the capacitor positive electrode.

The battery of this Example can contain further alternating positive andnegative electrodes of any type. Generally it is desirable to ensurethat there is some level of matching the surface areas and hydrogengassing rates of the sum of the positive and negative electrodes, and toinclude the requisite number of positive and negative electrodes toprovide a battery of the desired voltage.

Thus, many modifications may be made to the embodiments and examplesdescribed above without departing from the spirit and scope of theinvention.

1-75. (canceled)
 76. A hybrid battery-capacitor comprising: at least onebattery-type positive electrode, at least one battery-type negativeelectrode, at least one capacitor-type electrode selected from acapacitor negative electrode and a capacitor positive electrode, whereinthe capacitor negative electrode comprises a high surface area capacitormaterial and one or more additives selected from oxides, hydroxides orsulfates of lead, zinc, cadmium, silver and bismuth, and wherein thecapacitor positive electrode comprises: a high surface area capacitormaterial, Pb₂O₃, an oxide, hydroxide or sulfate of antimony, andoptionally one or more additives selected from oxides, hydroxides andsulfates of iron and lead, and an electrolyte in contact with theelectrodes, wherein a battery part is formed between the battery-typepositive electrode and the battery-type negative electrode, and anasymmetric capacitor part is formed between the capacitor electrode andone of the battery-type electrodes, wherein one of the battery-typeelectrodes is shared by the battery part and the asymmetric capacitorpart, and wherein the negative electrodes are in direct electricalconnection to a first conductor, and the positive electrodes are indirect electrical connection to a second conductor.
 77. The hybridbattery-capacitor of claim 76, wherein the battery-type positiveelectrode comprises an electrode material selected from lead dioxide,nickel oxide, silver oxide, manganese oxide, lithium polymer materials,mixed lithium oxides including lithium nickel oxides, lithium cobaltoxides, lithium manganese oxides and lithium vanadium oxides, andlithium conductive polymer cathode materials.
 78. The hybridbattery-capacitor of claim 76, wherein the battery-type negativeelectrode comprises an electrode material selected from lead, zinc,cadium, metal hydrides, lithium in metal or alloy form with other metalssuch as aluminium, and lithium ion intercalation materials.
 79. Thehybrid battery-capacitor of claim 76, wherein the electrodes alternatebetween positive and negative electrodes.
 80. The hybridbattery-capacitor of claim 76, wherein the high surface area material isa high surface area carbon material.
 81. The hybrid battery-capacitor ofclaim 76, wherein the capacitor-type electrode is a capacitor negativeelectrode, and the additive includes at least one oxide, hydroxide orsulfate of lead or zinc.
 82. The hybrid battery-capacitor of claim 81,wherein the additive is present in a coating on the capacitor negativeelectrode in an amount that increases the voltage window of thecapacitor negative electrode to at least −1.2V.
 83. The hybridbattery-capacitor of claim 81, wherein the total additive content isbetween 5-40 wt %, based on the total capacitor coating composition. 84.The hybrid battery-capacitor of claim 81, wherein the negative capacitorelectrode additive comprises compounds of the following metals in oxide,sulfate or hydroxide from: between 1-40 wt % Pb; 1-20 wt % Zn; 0-5 wt %Cd and 0-5 wt % Ag.
 85. The hybrid battery-capacitor of claim 76,wherein the capacitor-type electrode is a capacitor positive electrode,and the capacitor positive electrode additive is present in an amount of5-40 wt %.
 86. The lead-acid battery of claim 85, wherein the positivecapacitor electrode additive comprises between 0-30 wt % Pb in oxide,sulfate or hydroxide form, 1-10 wt % Pb2O3, 0-2 wt % Fe in oxide,sulfate or hydroxide form and 0.05 to 1 wt % Sb in oxide, sulfate orhydroxide form.
 87. The hybrid battery-capacitor of claim 76, whereinthe hybrid battery-capacitor comprises both a capacitor positiveelectrode and a capacitor negative electrode.
 88. The hybridbattery-capacitor of claim 76, wherein each of the positive and negativeelectrodes is separated from adjacent electrodes by porous separators.89. A capacitor negative electrode comprising a current collector and apaste coating, the paste coating comprising a high surface areacapacitor material, a binder and between 5-40 wt %, based on the weightthe paste coating, of an additive or additive mixture selected fromoxides, hydroxides or sulfates of lead, zinc, cadmium, silver andbismuth, with the proviso that the additive includes at least one oxide,hydroxide or sulfate of lead or zinc.
 90. A capacitor positive electrodecomprises a current collector and a paste coating, the paste coatingcomprising a high surface area capacitor material, a binder and between10-40 wt %, based on the weight the paste coating, of an additivemixture comprising: Pb₂O₃, an oxide, hydroxide or sulfate of antimony,and optionally one or more oxides, hydroxides or sulfates of iron andlead.
 91. An asymmetric capacitor comprising a capacitor negativeelectrode according to claim 89, or a capacitor positive electrode asdefined above, a battery-type electrode chose from lead or lead dioxideelectrode, and an electrolyte.
 92. A lead-acid battery comprising analternating series of positive and negative electrodes and anelectrolyte in contact with the electrodes, wherein: at least one pairof positive and negative electrodes or electrode regions store energycapacitively, and one of said electrodes or regions comprises capacitorelectrode material; at least one pair of lead dioxide positive and leadnegative battery electrodes or electrode regions store energyelectrochemically, the electrolyte is a sulfuric acid electrolytesolution, and wherein the positive electrodes are directly connected bya first conductor and the negative electrodes are directly connected bya second conductor.